Synergistic Influence of Tool Pin Geometry and Axial Force on Microstructure and Mechanical Performance of A356 Aluminium Alloy Friction Stir Welds

This study presents an investigation on the effect of tool pin profile and axial force on the mechanical and microstructural properties of friction stir welded A356 aluminium alloy joints while keeping rotational speed and welding speed constant. Experiments were conducted using three different tool pin profiles (cylindrical, tapered, and threaded) and three axial force levels (4, 6, and 8 kN). The welded joints were evaluated in terms of tensile strength, microhardness and impact strength. Results indicate that threaded pin profile combined with moderate axial force (6 kN) produced defect-free joints with superior mechanical performance. The study demonstrates that tool geometry and axial force play a critical role in improving joint quality in friction stir welding of A356 aluminium alloy.